Exposure mode selectro for automatically selecting automatic exposure control mode for electrophotographic copying machine

ABSTRACT

An electrophotographic copying machine of the type in which an automatic exposure control mode and a manual exposure control mode can be selected, includes an automatic exposure control mode selection circuit for automatically selecting the automatic control mode. The automatic exposure control mode selection circuit serves to automatically select the automatic exposure control mode in response to the start of power supply or after the copying machine is left unoperated for a predetermined length of time. A timer is provided for counting this predetermined time. For a copying machine of a magnification-changeable type, the automatic exposure control mode selection circuit is operated to automatically select the automatic exposure control mode in response to the selection of magnification.

BACKGROUND OF THE INVENTION

The present invention relates to an electrophotographic copying machineand, more particularly, to an exposure mode selecting circuit forautomatically selecting an automatic exposure control mode for anelectrophotographic copying machine.

An electrophotographic copying machine produces an electrostatic latentimage on a photoreceptor using an optical system. The latent imagecorresponds to an image on a copy document such as a manuscript or bookto be copied. A developing device is provided so that tone particles areelectrically adhered to the latent image, so that the latent imagebecomes visible as a toner image. The toner image is transferred onto acopy paper via a corona transference charger.

Conventionally, the light exposure of the electrophotographic copyingmachine is controlled depending on the shade of the copy document to becopied. For this purpose, a manual switch for controlling the lightexposure has been provided for a manual exposure control mode. Recently,an improved copying machine has been proposed including an automaticexposure controller for automatically controlling the light exposure,the controller being used for an automatic exposure control mode. Insuch a case, a mode switch is provided for selecting the manual exposurecontrol mode and the automatic exposure control mode. To select eithermode, this switch must be operated. Sometimes, it may be troublesome tohave to operate this switch. Further, before the copying operation isstarted, the operator must check the selection of this mode switch,resulting in an extra task.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animproved electrophotographic copying machine for automatically selectingan automatic exposure control mode.

It is another object of the present invention to provide an improvedelectrophotographic copying machine for automatically selecting anautomatic exposure control mode when the copying machine is leftunoperated for a predetermined length of time after a previousoperation.

It is a further object of the present invention to provide an improvedmagnification-changeable type electrophotographic copying machine forautomatically selecting an automatic exposure control mode in responseto changing magnification of the copying machine.

Briefly described, in accordance with the present invention, anelectrophotographic copying machine of the type which functions as amanual exposure control mode and an automatic exposure control mode,includes an automatic exposure control mode selection device forforcibly selecting the automatic exposure control mode in response tothe start of power supply. There may be further provided a timer forcounting a predetermined time after the operation of the copyingmachine, and an additiinal automatic exposure control mode selectorresponsive to the timer for forcibly selecting the automatic exposurecontrol mode after the lapse of the predetermined time. The timer isreset when the automatic exposure control mode selection means isoperated during a noncopying cycle, or after the completion of anycopying cycle. The timer is set after the reset operation or upon thestart of the power supply.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention and wherein:

FIG. 1 is a diagram of an automatic mode selection circuit forautomatically selecting an automatic exposure control mode for anelectrophotographic copying machine according to a first preferredembodiment of the present invention; and

FIG. 2 is a diagram of an automatic exposure mode selection circuit forautomatically selecting an automatic exposure control mode for amagnification-changeable type electrophotographic copying machineaccording to a second preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a diagram of an automatic exposure mode selection circuit forautomatically selecting an automatic exposure control mode for anelectrophotographic copying machine according to a first preferredembodiment of the present invention.

A mode selector is provided for selecting either an automatic exposurecontrol mode in which a light exposure amount is automatically selected,or a manual exposure control mode in which a light exposure amount ismanually selected. The mode selector includes a keep relay RL containinga set terminal S and a reset terminal R. While the keep relay RL is set,the automatic exposure control mode is selected. On the other hand,while it is reset, the manual exposure control mode is selected. Whenthe automatic exposure control mode is selected, the copying machine canoptically detect the shade of a copy document to be copied, so thatdepending on the detected shade, the light exposure amount can beautomatically controlled. The document is mounted on a document table.

Several methods of automatically controlling the light exposure areproposed. One of them is as follows: A slit is formed on the documenttable. Under the slit, a photosensitive sensor is disposed. A reflectedlight from the document passing through the slit is detected by thephotosensitive sensor, to determine the shade of the corresponding partof the document. Depending on the shade, a voltage to be applied to alight source is changed. This control is carried out over the totalareas of the document which is relatively moved, so that an optimumlight exposure amount for each part of the document can be selected.

To afford the manual exposure control mode, a plurality of voltagelevels to be applied to the driving source are changeable at a number ofsteps. A light exposure control switch disposed on a control panel ofthe copying machine is operated to desirably select one of the numerouslevels.

Because some specific examples of the automatic exposure control and themanual exposure control are conventional, any further description isomitted. The light exposure mode setting circuit of the presentinvention can be applied to any type of light exposure control device aslong as it can function as the automatic exposure control mode and themanual exposure control mode.

A mode selection switch circuit 1 includes two switches SW2 and SW3. Anautomatic exposure control mode selection switch SW2 is provided in thecontrol panel of the copying machine. This switch SW2 is operated toforcibly set the keep relay RL. A manual exposure control mode selectionswitch SW3 is also disposed in the control panel of the copying machine.This switch SW3 is operated to forcibly reset the keep relay RL. Themode selection switch circuit 1 is electrically coupled to a sourcevoltage VB via s switch SW1. Only while the switch SW1 is conductive,the switch circuit 1 is placed in an operable condition. The switchcircuit 1 is operated in conjunction with the operation of the copyingmechanism of the copying machine, so that it is not conductive duringthe copying cycle while it is conductive in the absence of a copyingcycle. The switch SW1 is operated to enable the power supply of thepower source VB to the mode selection switch circuit 1, a timer 4, and atime passage mode selection circuit 3.

An automatic exposure mode setting circuit 2 is operated upon the startof power supply. This circuit 2 is electrically coupled to a setterminal S of the keep relay RL via a diode D3. This mode settingcircuit 2 includes a transistor TR3, resistances R10 and R11, and acondenser C2 to form a circuit having a time constant for charge. Uponthe power supply, this mode setting circuit 2 provides a one-shot pulseto be inputted to the set terminal S of the keep relay RL.

An automatic exposure control mode setting circuit 3 is operated upon apassage of a predetermined time. This mode setting circuit 3 iselectrically coupled to the set terminal S of the keep relay RL via adiode D4. This mode setting circuit 3 includes a comparator forcomparing the output of the timer 4 and a reference voltage, atransistor TR2 connected to the output side of the comparator C, andsome resistances. The reference voltage is formed by dividing the sourcevoltage VB by resistances R6 and R7. The comparator C is operated insuch a manner that when the reference voltage applied to a positiveinput terminal "+" thereof is more than the output voltage of the timer4 applied to a negative input terminal "-" thereof, the transistor TR2is placed not conductive. On the other hand, when the output level ofthe timer 4 is more than the reference voltage, the transistor TR2 isplaced conductive. Thus, the automatic exposure control mode settingcircuit 3 forcibly sets the keep relay 3 upon the passage of thepredetermined time when the output level of the timer 4 exceeds thereference voltage.

The timer 4 includes a CR charge circuit. When a transistor TR1 isconductive, a charge current flows into a condenser C1 from the sourcevoltage VB through a diode D1 and a variable resistance VR, so that theoutput voltage of the condenser C1, namely, the output voltage of thetimer 4 is increased. A resistance R3 functions to discharge the chargesof the condenser C1. When the transistor TR1 is turned OFF, the chargesof the condenser C1 are abruptly discharged to reset the timer 4. Aswitch SW4 is interconnected between the base of the transistor TR1 andthe ground to become conductive when some specific conditions occur suchas the generation of paper jam conditions and the replacement of adeveloping agent or the like.

A switch operation detection circuit 5 is provided for detecting theoperation of the mode selection switch circuit 1. This detection circuit5 can detect the operation of the automatic exposure mode selectionswitch SW2 and the manual exposure selection switch SW3 duringconditions other than the copying cycles. When the circuit 5 detectssuch a condition, it permits the charges of the condenser C1 to beabruptly discharged to thereby reset the timer 4. Thus, when either theswitch SW2 or the switch SW3 is operated, the transistor TR4 becomesconductive to abruptly discharge the charges of the condenser C1 throughthe resistance R14 and the transistor TR4.

In operation, once the power voltage is supplied, the automatic exposuremode selection circuit 2 is operated to forcibly set the keep relay RL,so that the copying machine is placed in the automatic exposure controlmode. At the same time, the switch SW1 is conductive so that thecondenser C1 is started to be charged to start the counting of the timer4. When such a condition is left without change and the charges of thecondenser C1 exceed the reference voltage applied to the negative inputterminal of the comparator C, the transistor TR2 of the automaticexposure mode setting circuit 3 upon the passage of the predeterminedlength of time becomes conductive, so that the keep relay RL is forciblyset via the diode D4. That is, if the copying machine is left unoperatedfor a predetermined length of time after the power voltage supply, thepredetermined length of time being defined by the charge circuit of thecondenser C1, it is forcibly set in the automatic exposure moderegardless of the previous exposure mode.

If the manual exposure mode selection switch SW3 is operated within thepredetermined length of time, the keep relay RL is reset so that thecopying machine is set in the manual exposure selection mode. At thesame time, the switch operation detection circuit 5 is operated toabruptly discharge the charges of the condenser C1, whereby the timer 4is reset. After the timer 4 is reset, the condenser C1 is started to becharged. Then, if the copying machine is left without operation for thepredetermined length of time, the keep relay RL is forcibly set, again.

After the copying operation has been completed in either the automaticexposure control mode or the manual exposure control mode, the switchSW1 is turned ON. Upon the ON condition of this switch, the condenser C1of the timer 4 is started to be charged. That is, this is the samecondition of the power supply start. The transistor TR2 becomesconductive if the copying machine is left unoperated until the condenserC1 is charged to a predetermined voltage level, whereby the keep relayRL is set. Thereafter, to select the manual exposure control mode, theswitch SW3 is operated to reset the keep relay RL.

If any copying operation is started under the condition that the switchSW1 is conductive, but the charging voltage to the condenser C1 is notup to the reference voltage, the switch SW1 becomes unconductive, sothat the charging of the condenser C1 is stopped and the charges of thecondenser C1 are abruptly discharged to thereby reset the timer 4.Therefore, in the case of reopening the copying operation within thepredetermined time during the manual exposure control mode, the keeprelay RL is prevented from receiving a set signal.

When the copying machine is left without operation after the completionof the copying cycle, the keep relay RL is set in the same manner asabove described.

Thus, the timer 4 is automatically started upon the power voltage supplystart or after its reset condition. When the mode selection switch isactuated during the cases other than the copying cycle, or the copyingcycle has been completed, the timer 4 is reset. The keep relay RL isforcibly set when it is left without being operated for a predeterminedtime after the start of the timer 4, or upon the power supply start.Thus, even if the manual exposure control mode is selected to conductthe copying operation, but the copying machine is left unoperated for apredetermined length of time, the automatic exposure control mode isautomatically returned.

The automatic exposure control mode is automatically selected in anyoneof the following conditions:

1. When the document to be copied has a normal shade, in other words,the automatic exposure control mode should be more frequently used thanthe manual exposure control mode.

2. A next copying operation is not conducted within a predeterminedlength of time after some copying operation has been completed.

3. The manual exposure control mode is not selected within apredetermined length of time after having selected the manual exposurecontrol mode.

4. The power source is started to be supplied.

Therefore, normally, the operator can assume that the copying machine isplaced in the automatic exposure control mode in conducting the copyingoperation. He can ignore setting the light exposure control. Anypossible mis-copy due to the light exposure control can be eliminated.

Another preferred embodiment of the present invention in which a copymagnification changeable type electrophotographic copying machinecomprises an exposure setting circuit for forcibly setting the exposurecontrol mode setting switch circuit in the automatic exposure controlmode in response to the actuation of a magnification selection switch.

FIG. 2 is a configuration of a mode setting circuit of a magnificationchangeable electrophotographic copying machine according to a secondpreferred embodiment of the present invention.

Three scale control switches SW11-SW13 and two mode selection switchesSW14 and SW15 are disposed in the control panel of the copying machine.The first scale switch SW11 is operated to select an equal-size copymode. The second scale switch SW12 is operated to select a reductioncopy mode. The third scale switch SW13 is operated to select amagnification copy mode. The switch SW14 is actuated to select theautomatic exposure control mode. The switch SW15 is actuated to selectthe manual exposure control mode.

The three scale switches SW11-SW13 are connected to set terminals S1-S3of scale setting keep relays RL1-RL3, respectively. The scale settingkeep relays RL1-RL3, when set, select the equal-scale copy mode, thereduction mode, and the magnification mode, respectively. While each ofthe scale switches SW11-SW13 is connected to one of the set terminals ofthe scale setting keep relays SW11-SW13, each of the scale switchesSW11-SW13 is connected to a reset terminal of each of the remainingscale setting keep relays. Then, when anyone of the scale switchesSW11-SW13 is actuated, only the keep relay having the set terminalconnected to the actuated scale switch is set. For example, the scaleswitch SW11 is connected to a set terminal S1 of the keep relay RL1while it is connected to reset terminals RL2 and RL3 of the keep relaysRL2 and RL3. If either the keep relay RL2 or the keep relay RL3 is set,the scale switch SW11 is operated so that either the keep relay RL2 orthe keep relay RL3 of each set is reset and only the keep relay RL1 isset. Similarly, when the scale switch S12 is operated, only the scalesetting keep relay R12 is set. When the scale switch SW13 is operated,only the scale setting keep relay RL3 is set. A central processing unit(CPU) may be provided for detecting the set conditions of the scalesetting relays RL1-RL3. The CPU is provided for controlling theoperation of the copying machine. In response to the set conditionsdetected, an optical scanning system is adjusted. The magnificationcontrol system for adjusting the optical system may be conventional.

The mode selection switch assembly includes the automatic exposurecontrol mode selection switch SW14 and the manual exposure control modeselection switch SW15. These switches SW14 and SW15 are connected to aset terminal S4 and a reset terminal R4 of an exposure control modesetting keep relay RL4, respectively. The exposure control mode settingkeep relay RL4 functions to select either the automatic exposure controlmode or the manual exposure control mode. When the keep relay RL4 isset, the automatic exposure control mode is selected. While it is reset,the manual exposure control mode is selected.

As similar to the above-described preferred embodiment, during theautomatic exposure control mode, the copying machine can opticallydetect the shade of the document to be copied and mounted on thedocument table. The light exposure is controlled based on the shadedetected.

The keep relay RL4 is set by the automatic exposure control mode settingswitch SW14 and reset by the manual exposure control mode setting switchSW15. To the set terminal S4 of the keep relay RL4, an automaticexposure control mode selection circuit 11 and a power-supply start modeselection circuit 12 are connected. The automatic exposure control modeselection circuit 11 includes diodes D20-D22, respectively, connected tothe scale switches SW11-SW13. When anyone of these scale switchesSW11-SW13 is actuated, the keep relay RL4 is forcibly set. The powersupply start mode selection circuit 12 forms a one-shot pulse inresponse to the start of the power supply, so that the one-shot isapplied to the set terminal S4 of the keep relay RL4 to thereby forciblyset the keep relay RL4.

Thus, according to the present invention, when anyone of the scaleswitches SW11-SW13 is operated, the exposure mode selection keep relayRL4 is forcibly set, regardless of whether either the automatic exposurecontrol mode or the manual exposure control mode has been alreadyselected, whereby the automatic exposure control mode is automaticallyselected in the copying machine. In other words, when the magnificationis changed in the copying machine, the automatic exposure control modeis necessarily selected.

In the above second preferred embodiment of the present invention, it isdescribed that, to return the automatic exposure control mode afterselecting the manual exposure control mode, the scale switches SW11-SW13or the automatic exposure selection switch SW14 must be operated.However, it may be possible that a timer is provided for starting thetiming counting operation after the copying operation regardless of theselected exposure control mode, and automatically returning the copyingmachine to the automatic exposure control mode after the copying machineis left unoperated for a predetermined length of time. Such a timer maybe easily provided with reference to the teaching of the first preferredembodiment of the present invention.

According to the feature of the second preferred embodiment of thepresent invention, the operator can assume after changing themagnification that the automatic exposure control mode is necessarilyselected. Further, when the power supply is started, the power supplystart mode setting circuit 2 is automatically operated to forcibly setthe exposure mode selection keep relay RL4, so that the automaticexposure control mode is automatically selected.

While only certain embodiments of the present invention have beendescribed, it will be apparent to those skilled in the art that variouschanges and modifications may be made therein without departing from thespirit and scope of the present invention as claimed.

What is claimed is:
 1. An electrophotographic copying machine comprising:exposure control means for controlling the exposure during a copying operation of the electrophotographic copying machine by varying the intensity of light supplied to expose a copy document, said means for controlling being operable in an automatic exposure control mode in which an amount of light supplied to expose the copy document is automatically determined and a manual exposure control mode in which an amount of light supplied to expose the copy document is manually set; first means for automatically selecting said automatic exposure control mode of said exposure control means in response to an initial supply of power to said copying machine; manual switch means for selecting between the automatic exposure control mode and the manual exposure control mode of said exposure control means; means for counting a predetermined length of time after the occurrence of the copying operation in either of the automatic exposure control mode or the manual exposure control mode,said means for counting being reset when said automatic exposure selection control mode is selected during a non-copying cycle, or after the completion of any copying cycle, said means for counting being set after said reset operation or upon the initiation of the supply of power to said copying machine; and second means for automatically selecting said automatic exposure control mode in response to the lapse of said predetermined length of time.
 2. The copying machine of claim 1, further including a magnification control switch for selecting a copy magnification level.
 3. The copying machine of claim 2, wherein said second means for automatically selecting said automatic exposure control mode is operated in response to an operation of said magnification control switch.
 4. The copying machine of claim 1, wherein said means for counting a predetermined length of time is a RC time constant charge circuit. 